From patchwork Wed Nov 16 13:48:32 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Emanuele Giuseppe Esposito X-Patchwork-Id: 13045231 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A72EDC433FE for ; Wed, 16 Nov 2022 13:50:48 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ovImo-0000dP-82; Wed, 16 Nov 2022 08:49:06 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ovImm-0000cP-EI for qemu-devel@nongnu.org; Wed, 16 Nov 2022 08:49:04 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ovImg-0007zF-Hw for qemu-devel@nongnu.org; Wed, 16 Nov 2022 08:49:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668606537; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=r+63Rvz1O2BCywQdimBwCPmeQIwX6qzesR//g/fyLJg=; b=SPpihc3PF58AvlVmOZxUf8QswTJuZUNfXB/XJaCrjLtvFgIzQUH8dNn3dXDlZcZbhs9sJQ ZWUVQNcWerNcPKrRO8NFci8Q3hiSu/NTfVstmS70YQbXmmxfIk+4c/tgEl8xNtZ6N3I8/J RYUE/1bDosJ9ZvdjBscXXQ2mbZIIYMg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-670-ZYHaDMSfMM2TShOgAMNDyA-1; Wed, 16 Nov 2022 08:48:53 -0500 X-MC-Unique: ZYHaDMSfMM2TShOgAMNDyA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D45B7185A78B; Wed, 16 Nov 2022 13:48:52 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 877054A9254; Wed, 16 Nov 2022 13:48:52 +0000 (UTC) From: Emanuele Giuseppe Esposito To: qemu-block@nongnu.org Cc: Kevin Wolf , Hanna Reitz , John Snow , Paolo Bonzini , Vladimir Sementsov-Ogievskiy , Stefan Hajnoczi , Fam Zheng , Eric Blake , Cleber Rosa , qemu-devel@nongnu.org, Emanuele Giuseppe Esposito Subject: [PATCH 02/20] graph-lock: introduce BdrvGraphRWlock structure Date: Wed, 16 Nov 2022 08:48:32 -0500 Message-Id: <20221116134850.3051419-3-eesposit@redhat.com> In-Reply-To: <20221116134850.3051419-1-eesposit@redhat.com> References: <20221116134850.3051419-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eesposit@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Just a wrapper to simplify what is available to the struct AioContext. Signed-off-by: Emanuele Giuseppe Esposito --- block/graph-lock.c | 59 ++++++++++++++++++++++++++------------ include/block/aio.h | 12 ++++---- include/block/graph-lock.h | 1 + 3 files changed, 48 insertions(+), 24 deletions(-) diff --git a/block/graph-lock.c b/block/graph-lock.c index b608a89d7c..c3c6eeedad 100644 --- a/block/graph-lock.c +++ b/block/graph-lock.c @@ -44,12 +44,23 @@ static uint32_t orphaned_reader_count; /* Queue of readers waiting for the writer to finish */ static CoQueue reader_queue; +struct BdrvGraphRWlock { + /* How many readers are currently reading the graph. */ + uint32_t reader_count; + + /* + * List of BdrvGraphRWlock kept in graph-lock.c + * Protected by aio_context_list_lock + */ + QTAILQ_ENTRY(BdrvGraphRWlock) next_aio; +}; + /* - * List of AioContext. This list ensures that each AioContext + * List of BdrvGraphRWlock. This list ensures that each BdrvGraphRWlock * can safely modify only its own counter, avoid reading/writing * others and thus improving performances by avoiding cacheline bounces. */ -static QTAILQ_HEAD(, AioContext) aio_context_list = +static QTAILQ_HEAD(, BdrvGraphRWlock) aio_context_list = QTAILQ_HEAD_INITIALIZER(aio_context_list); static void __attribute__((__constructor__)) bdrv_init_graph_lock(void) @@ -60,29 +71,31 @@ static void __attribute__((__constructor__)) bdrv_init_graph_lock(void) void register_aiocontext(AioContext *ctx) { + ctx->bdrv_graph = g_new0(BdrvGraphRWlock, 1); QEMU_LOCK_GUARD(&aio_context_list_lock); - assert(ctx->reader_count == 0); - QTAILQ_INSERT_TAIL(&aio_context_list, ctx, next_aio); + assert(ctx->bdrv_graph->reader_count == 0); + QTAILQ_INSERT_TAIL(&aio_context_list, ctx->bdrv_graph, next_aio); } void unregister_aiocontext(AioContext *ctx) { QEMU_LOCK_GUARD(&aio_context_list_lock); - orphaned_reader_count += ctx->reader_count; - QTAILQ_REMOVE(&aio_context_list, ctx, next_aio); + orphaned_reader_count += ctx->bdrv_graph->reader_count; + QTAILQ_REMOVE(&aio_context_list, ctx->bdrv_graph, next_aio); + g_free(ctx->bdrv_graph); } static uint32_t reader_count(void) { - AioContext *ctx; + BdrvGraphRWlock *brdv_graph; uint32_t rd; QEMU_LOCK_GUARD(&aio_context_list_lock); /* rd can temporarly be negative, but the total will *always* be >= 0 */ rd = orphaned_reader_count; - QTAILQ_FOREACH(ctx, &aio_context_list, next_aio) { - rd += qatomic_read(&ctx->reader_count); + QTAILQ_FOREACH(brdv_graph, &aio_context_list, next_aio) { + rd += qatomic_read(&brdv_graph->reader_count); } /* shouldn't overflow unless there are 2^31 readers */ @@ -138,12 +151,17 @@ void bdrv_graph_wrunlock(void) void coroutine_fn bdrv_graph_co_rdlock(void) { - AioContext *aiocontext; - aiocontext = qemu_get_current_aio_context(); + BdrvGraphRWlock *bdrv_graph; + bdrv_graph = qemu_get_current_aio_context()->bdrv_graph; + + /* Do not lock if in main thread */ + if (qemu_in_main_thread()) { + return; + } for (;;) { - qatomic_set(&aiocontext->reader_count, - aiocontext->reader_count + 1); + qatomic_set(&bdrv_graph->reader_count, + bdrv_graph->reader_count + 1); /* make sure writer sees reader_count before we check has_writer */ smp_mb(); @@ -192,7 +210,7 @@ void coroutine_fn bdrv_graph_co_rdlock(void) } /* slow path where reader sleeps */ - aiocontext->reader_count--; + bdrv_graph->reader_count--; aio_wait_kick(); qemu_co_queue_wait(&reader_queue, &aio_context_list_lock); } @@ -201,11 +219,16 @@ void coroutine_fn bdrv_graph_co_rdlock(void) void coroutine_fn bdrv_graph_co_rdunlock(void) { - AioContext *aiocontext; - aiocontext = qemu_get_current_aio_context(); + BdrvGraphRWlock *bdrv_graph; + bdrv_graph = qemu_get_current_aio_context()->bdrv_graph; + + /* Do not lock if in main thread */ + if (qemu_in_main_thread()) { + return; + } - qatomic_store_release(&aiocontext->reader_count, - aiocontext->reader_count - 1); + qatomic_store_release(&bdrv_graph->reader_count, + bdrv_graph->reader_count - 1); /* make sure writer sees reader_count before we check has_writer */ smp_mb(); diff --git a/include/block/aio.h b/include/block/aio.h index 8e64f81d01..0f65a3cc9e 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -22,6 +22,7 @@ #include "qemu/event_notifier.h" #include "qemu/thread.h" #include "qemu/timer.h" +#include "block/graph-lock.h" typedef struct BlockAIOCB BlockAIOCB; typedef void BlockCompletionFunc(void *opaque, int ret); @@ -127,14 +128,13 @@ struct AioContext { /* Used by AioContext users to protect from multi-threaded access. */ QemuRecMutex lock; - /* How many readers in this AioContext are currently reading the graph. */ - uint32_t reader_count; - /* - * List of AioContext kept in graph-lock.c - * Protected by aio_context_list_lock + * Keep track of readers and writers of the block layer graph. + * This is essential to avoid performing additions and removal + * of nodes and edges from block graph while some + * other thread is traversing it. */ - QTAILQ_ENTRY(AioContext) next_aio; + BdrvGraphRWlock *bdrv_graph; /* The list of registered AIO handlers. Protected by ctx->list_lock. */ AioHandlerList aio_handlers; diff --git a/include/block/graph-lock.h b/include/block/graph-lock.h index f975312bb6..fc806aefa3 100644 --- a/include/block/graph-lock.h +++ b/include/block/graph-lock.h @@ -53,6 +53,7 @@ * reader count. In that case we transfer the count to a global shared counter * so that the writer is always aware of all readers. */ +typedef struct BdrvGraphRWlock BdrvGraphRWlock; /* * register_aiocontext: